When placed in the terrestrial magnetic field, the electron beams emitted by the electron gun in a cathode ray tube are subject to an excess Lorentz force due to the terrestrial magnetic field. Thus, the movement of the electrons shifts several dozen μm away from the regular trajectory, so that it does not hit the fluorescent material on the screen properly, and so-called “mislanding” occurs. Such electron beam shifts cause color deviations and color irregularities on the screen.
In cathode ray tubes for flat TVs, which are becoming the mainstream in recent years, the shadow mask sheet is often stretched under the application of tensile forces to increase the flatness of the screen. But when the shadow mask is stretched with high tensile forces, the electron beam shifts increase, and color deviations and color irregularities become even worse. Thus, there is a demand for a way to effectively correct for the terrestrial magnetism in cathode ray tubes for flat TVs.